Production and reproduction norms of fine woolled Merino sheep on natural pastures in the Karoo

INTRODUCTION

During the past two decades there was a shift in the emphasis regarding the demand of wool, away from control wool to fine wool. The proportion of fine wool (20 µm and finer) in the national clip, however, decreased from 69% in 1951/55 to only 4% in 1976/80 (Marx, 1981). This decrease was mainly due to more emphasis being placed on the selection for the amount of wool produced in the 1950's and 1960's.

The price premium paid for finer wool during the 1980's lead to more emphasis being placed on the production of fine wool, rather than simply the amount of wool. The increased demand for finer wool and the associated price difference caused the proportion of fine wool (20 µm and finer) in the national clip to increase to 9.71% in 1998/99 (Ona Viljoen - Personal communication).

This shift in the emphasis of wool production caused more attention to be given to the production of fine wool types and lead to the establishment of fine wool projects at the Cradock Experimental Station and at Grootfontein Agricultural Development Institute.

With the increased demand for fine wool, there is a tendency to produce this type of wool under less favourable feeding conditions. The general opinion is, however, that this type of wool cannot be effectively produced under the extensive and arid farming conditions of South Africa. It is widely known that several wool quality factors such as fibre diameter, fibre length and tensile strength are influenced by the amount of nutrients available to the wool follicles. The amount of wool is in turn influenced by fibre diameter and -length (Reis & Sahlu, 1994). Several researchers indicated that the effect of nutrition on wool production is mainly expressed in fibre length and -diameter (Nichols, 1933; Galpin, 1948; Stewart et al., 1961).

Due to the shift in emphasis towards fine wool production and the general opinion about fine wool production under extensive farming conditions, the objective of this study was therefore to establish a fine wool flock at Grootfontein ADI in order to evaluate the production and reproduction performance of fine wool animals against a control group on natural pastures in the Karoo.

MATERIAL AND METHODS

In 1989, 400 Merino ewes with an average fibre diameter of 23.6 μm were randomly divided into two groups of 200 ewes each, a fine wool (F) and control (C) line. The F-line was upgraded by being mated to genetic fine woolled rams from the Grootfontein fine wool Merino stud, while the C-line was mated to rams from the Grootfontein Merino stud. In both cases, the rams used in the two lines were the same rams that were used in the respective studs.

Data collected from this flock from 1989 to 1999 were used for this analysis. The production traits analysed for the lambs included birth weight, weaning weight, 15-month body weight, greasy fleece weight, clean fleece weight, mean fibre diameter, clean yield, staple length, pleat score and number of crimps per 25 mm. The ewe flock was shorn each year. Due to the fact that the ewes were being upgraded, the production traits of 1997 and 1998 of the ewe flock were used for the purpose of this study. The same wool traits were analysed as for the lambs.

The reproduction traits analysed were conception rate, lambing percentage, weaning percentage, survival rate and total weight of lamb weaned (TWW) over a ewe’s lifetime. Both lines had three lambing opportunities on average.

The following fixed effects were included in the model for birth weight: sex, birth status, age of dam (years), year of birth, line (F or C) and the two-way interaction of sex*line. For weaning weight the following effects were included: sex, rearing status (combination of birth and weaning status), age of dam, year of birth, line and the two-way interaction of sex*line. The age of the animals (linear regression) at weaning was also included in the model. The same effects as for weaning weight, except the age of the animals, were included in the models for the 15-month body weight and the fleece traits. For the production traits of the ewe flock, only year and line were used in all the models. For TWW, fixed effects of line and number of lambing opportunities were included in the model.

The least squares means (LSM) and the standard errors for the production traits and for TWW were obtained with the PROC GLM-procedure of SAS and the significance levels between the sexes and flocks were obtained with the PDIFF-option under the PROC GLM-procedure of SAS (Littell et al., 1991). The line differences in conception rate, lambing percentage, weaning percentage and survival rate were tested for significance with the CHI-SQUARE-procedure of SAS (SAS, 1990).

RESULTS AND DISCUSSION

The LSM and standard errors for the body weights and fleece traits are presented in Table 1. It is evident from this table that the birth weight of the control lambs differed significantly from the fine wool lambs. There was no significant difference in weaning weight between the lines. However, at 15-months of age the control lambs were heavier (P<0.05) than the fine wool lambs.

Table 1. The least squares means of the body weights and fleece traits of the ram and ewe lambs

It is evident from this table that the lambs of the fine woolled line produced significantly less and finer wool when compared to their contemporaries in the control line. The clean yield of the control animals was also higher (P<0.05) than that of the fine woolled animals. There was no significant difference in the staple length of the ram lambs, while the control ewe lambs had significantly longer staples than the fine woolled ewe lambs. The pleat score also did not differ significantly between the two lines. The lambs of the F-line had more (P<0.05) crimps per 25mm than the C-line lambs.

The least squares means and standard errors of the production traits of the ewe flock are summarised in Table 2. From this table it is evident that there was no significant difference between the body weights of the two lines. The respective clean fleece weights of the F- and C-lines were 3.16 ± 0.04 kg and 3.51 ± 0.04 kg (P<0.05) and the respective values for mean fibre diameter were 19.65 ± 0.11 μm and 21.61 ± 0.12 μm (P<0.05). The fine woolled ewes had also significantly more crimps per 25 mm than the control ewes. There were no significant differences in clean yield, staple length or pleat score between the lines. The decrease in the mean fibre diameter of the control flock can be ascribed to the fact that the main selection criteria in the Grootfontein Merino stud were increased body weight and decreased fibre diameter.

Table 2. The least squares means and standard errors of the production data of the ewe flock.

Fine woolled ewes

Control ewes

Body weight (kg)

50.45 ± 0.39

51.01 ± 0.40

Greasy fleece weight (kg)

5.04 a ± 0.06

5.43 a ± 0.06

Clean fleece weight (kg)

3.16 a ± 0.04

3.51 a ± 0.04

Mean fibre diameter (μm)

19.65 a ± 0.11

21.61 a ± 0.12

Clean yield (%)

66.29 ± 0.32

65.24 ± 0.33

Staple length (mm)

88.01 ± 0.76

87.56 ± 0.77

Pleat score

8.47 ± 0.07

8.46 ± 0.07

No. of crimps / 25 mm

13.84 a ± 0.11

9.13 a ± 0.11

a - Values with the same superscript differed significantly (P<0.05)

The conception rate (number of ewes lambed / number of ewes mated), lambing percentage (number of lambs born / number of ewes mated), weaning percentage (number of lambs weaned / number of ewes mated), survival rate (number of lambs weaned / number of lambs born alive) and least squares means of TWW are presented in Table 3. Although the conception rate of the two lines was approximately the same, slightly more lambs were born in the C-line (133%) compared to the F-line (129%). However, in the F-line more lambs were weaned per ewe mated (94% vs 92%) than in the C-line. The fact that the survival rate was relatively low in these two lines can be ascribed to two main factors. Firstly, most of the deaths of lambs prior to weaning can be ascribed to a Chlamydia infection where the ewes lambed on small, irrigated pastures. Secondly, stray dogs, as well as vermin also caused losses in some years. The least squares means of total weight of lamb weaned over a ewe’s lifetime were 92.57 ± 4.25 kg and 91.68 ± 4.20 kg respectively for the F- and C-lines.

Table 3. The conception rate, lambing percentage, weaning percentage and the least squares means and standard errors for total weight of lamb weaned

Fine woolled ewes

Control ewes

Conception rate (%)

88

89

Lambing percentage (%)

129

133

Weaning percentage (%)

94

92

Survival rate (%)

73

69

Total weight of lamb weaned (kg)

92.57 ± 4.25

91.68 ± 4.20

CONCLUSION

It is evident from the results of this study that the control lambs had a slightly better growth rate than the fine woolled lambs, however, the body weight and reproduction of the ewes were equal. The fine wool animals produced significantly less and finer wool compared to the control wool animals. Furthermore, it is evident that it is possible to produce finer wool under natural pastures in the Karoo. These fine woolled ewes are compared to the strong woolled animals of four participating farmers in the Carnarvon, De Aar, Steynsburg and Wakkerstroom areas in a new project.